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Principle of Segregation  Genes occur in pairs (like chromosomes).  During gamete production, members of each gene pair separate.  During fertilization, the full number of chromosomes is restored (allele pairs are reunited).  Homozygous- same allele at same locus on both members of a chromosome pair. (i.e.TT, tt)  Heterozygous- two different alleles at the same locus on a chromosome pair.

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Dominance And Recessiveness  Recessive traits are not expressed in heterozygotes.  For a recessive allele to be expressed, there must be two copies of the allele.  Dominant traits are governed by an allele that can be expressed in the presence of another, different allele.  Dominant alleles prevent the expression of recessive alleles in heterozygotes.

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Principle of Independent Assortment  The distribution of one pair of alleles into gametes does not influence the distribution of another pair.  The genes controlling different traits are inherited independently of one another.

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Mendelian Inheritance in Humans  Mendelian principles apply to over 4,500 human traits.  The human ABO blood system is an example of a simple Mendelian inheritance.  The A and B alleles are dominant to the O allele.  Neither the A or B allele are dominant to one another (codominant and both traits are expressed).

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Polygenic Inheritance  Polygenic traits are continuous traits governed by alleles at more than one genetic locus.  Continuous traits show gradations.  Skin color is a common example of a polygenic trait it is governed by 6 loci and at least 12 alleles.

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Mitochondrial Inheritance  Convert energy into a form that can be used by the cell.  Animals inherit their mtDNA (and mt traits) from their mothers.  All the variation in mtDNA is caused by mutation, which makes it very useful for studying genetic change over time.

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Heredity and Evolution  Evolution works at four levels:  Molecular  Cellular  Individual  Population  The levels reflect different aspects of evolution and are integrated in a way that produces evolutionary change.

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The Modern Synthesis Evolution is a two-stage process: 1. The production and redistribution of variation. 2. Natural selection acting on this variation (affect ability to reproduce & survive) Evolution = Mutation or Natural Selection

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A Current Definition Of Evolution  Modern Genetics: evolution= a change in allele frequency from one generation to the next.  Allele frequencies are indicators of the genetic makeup of an interbreeding group of individuals known as a population. Small changes + Time + Natural Selection= Evolution

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Mutation Mutation is a molecular alteration in genetic material:  For a mutation to have evolutionary significance it must occur in a gamete (sex cell).  Such mutations will be carried on one of the individual's chromosomes.  During meiosis the chromosome carrying the mutation will assort giving a 50% chance of passing the allele to an offspring.

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Gene Flow  Gene flow is the exchange of genes between populations.  If individuals move temporarily and mate in the new population (leaving a genetic contribution), they don’t necessarily remain in the population. Example: The offspring of U.S. soldiers and Vietnamese women.

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Genetic Drift  Genetic drift is directly related to population size.  Genetic drift occurs when some individuals contribute a disproportionate share of genes to succeeding generations.  Drift may also occur solely because the population is small:  Alleles with low frequencies may simply not be passed on to offspring, so they eventually disappear from the population.

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Founder Effect  Genetic drift in which allele frequencies are altered in small populations from larger populations.  A new population will be established. (all members will be descended from the founders)  An allele that was rare in the founders’ parent population but is carried by even one of the founders can eventually become common.  Example: French Canadians in Quebec

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Recombination  In sexually reproducing species both parents contribute genes to offspring.  The genetic information is reshuffled every generation.  Recombination doesn’t change allele frequencies, however, it does produce different combinations of genes that natural selection may be able to act on.

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Natural Selection  Natural selection provides directional change in allele frequency relative to specific environmental factors.  If the environment changes, selection pressures also change.  If there are long-term environmental changes in a consistent direction, then allele frequencies should also shift gradually each generation.

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Levels of Organization in the Evolutionary Process Evolutionary Factor LevelEvolutionary Process MutationDNA Storage of genetic information; ability to replicate; influences phenotype by production of proteins MutationChromosomes A vehicle for packaging and transmitting DNA

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1. Mendel used the term dominant for a) plants that were larger than others of the same variety. b) a trait that prevented another trait from appearing. c) a variety of pea plants that eliminated a weaker variety. d) a trait that "skipped" a generation.

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Answer: b  Mendel used the term dominant for a trait that prevented another trait from appearing.

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2. Genes exist in pairs in individuals; during the production of gametes, the pairs are separated so that a gamete has only one of each kind. This is known as the a) principle of segregation. b) principle of independent assortment. c) mitosis. d) unification theory.

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correct: a  Genes exist in pairs in individuals; during the production of gametes, the pairs are separated so that a gamete has only one of each kind. This is known as the principle of segregation.

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3. Traits that have a range of phenotypic expressions and show a continuum of variation are termed a) co-dominant. b) polygenic. c) polymorphic. d) sex-linked.

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Answer: b  Traits that have a range of phenotypic expressions and show a continuum of variation are termed polygenic.

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4. When alleles are introduced into a population from another population, this is known as a) genetic drift. b) gene flow/migration. c) founder effect. d) bottleneck effect.

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Answer: b  When alleles are introduced into a population from another population, this is known as gene flow/migration.

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5. The most complete definition of biological evolution is a) change. b) mutation. c) survival of the fittest. d) a change in allele frequency from one generation to the next.

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Answer: d  The most complete definition of biological evolution is a change in allele frequency from one generation to the next.